Book Description
We study the excitonic structure and optical properties of single quantum dots in three different II-VI semiconductor structure systems: as-grown CdSe/ZnSe, as-grown CdTe/ZnTe, and annealed CdTe/ZnTe self-assembled quantum dots(QD) using photoluminescence(PL), micro-PL, micro-PL obtained using a sub-wavelength aperture, and PL images obtained using a Solid Immersion Lens (SIL). These experiments are performed both at zero field and magnetic field up to 3 Tesla. While in zero field, linear polarized PL are used to find exchange splitting and QD asymmetry direction of the three QD samples, in a 3 Tesla magnetic field, circular polarized PL is used to determine the g-factor and diamagnetic shift. With a solid immersion lens (SIL), we are able to directly image a large number of single QD at 6K with 400 nm spatial resolution. Using zero field measurements, we find that while the some of the QDs are symmetric, and emit completely unpolarized light, over half of the QDs are antisymmetric which are typically aligned along one of the in-plane crystallographic directions, and so emit linear polarized PL. Since polarization properties as well as spin properties such as exchange splitting, g-factor and diamagnetic coefficient are different from dot to dot due to their size and asymmetry variations, we have carried out a statistical study of these properties in order to understand what changes occur in the QDs between these three samples. The major result from this work shows that thermal annealing of CdTe dots significantly reduces the statistical variation of exchange splittings for asymmetric dots as well as the g-factors for symmetric dots. We infer that these changes result from enlargement of the CdTe dots due to interdiffusion of Zn between the barriers and the dots. This enlargement is reflected in the increase of the median distributions of the diamagnetic shifts. Moreover, in CdSe dots, where the dot size is comparable or slightly larger than the exciton Bohr diameter, we find that the variation of these parameters is reduced as well.
